1. Field of the Invention
The invention relates to a sealed battery, and more particularly, to technology for sealing a through-hole open in a battery case.
2. Description of the Related Art
For a sealed battery such as a lithium-ion secondary battery or a nickel-metal-hydride secondary battery, a structure is typically known in which charge and discharge elements (such as a positive electrode, a negative electrode, and a separator and the like) are housed inside a battery case, and a filling hole that is a through-hole open in a cover portion is sealed after the battery case has been filled with electrolyte.
Japanese Patent Application Publication No. 2003-229118 (JP 2003-229118 A), for example, describes technology for sealing such a through-hole according to a method that involves using a blind rivet having a flange and a sleeve as a plug member, and sealing the through-hole by inserting the sleeve into the through-hole and then elastically deforming this sleeve so as to compress a gasket arranged between the flange and the through-hole, as shown in FIG. 9A.
However, with the plug member described in JP 2003-229118 A, when internal pressure of the battery rises, the area around the through-hole of the cover portion may deform outward, such that an inner peripheral end portion of the cover portion presses the gasket upward, as shown in FIG. 9B. At this time, the gasket is pushed out by radially outward force from the cover portion, as shown by arrows F0 in FIG. 9B. As a result, contact with the sleeve of the blind rivet becomes weak, possibly resulting in a decrease in strength and seal performance of the sealing portion.